Fluid tailings streams are typically by-products of mining operations that are composed of water and solid particles. In order to recover the water and consolidate the solids, solid/liquid separation techniques must be applied. In oil sands processing, there are different fluid tailings streams with different compositions. For example, a typical fresh tailings stream comprises water, sand, silt, clay, and residual bitumen. However, if the tailings stream is derived from a froth treatment process, it will also comprise residual solvents and other hydrocarbonaceous materials (e.g. asphaltenes).
Oil sands tailings typically comprise a substantial amount of fine particles (defined as solids that are less than 44 microns) and clays. The bitumen extraction process uses hot water and chemical additives such as sodium hydroxide or sodium citrate to remove the bitumen from the solid particles. The side effect of these chemical additives is that they change the inherent water chemistry and thus the solids in the aqueous phase acquire a negative charge. Due to strong electrostatic repulsion, the fine particles form a stabilized suspension that does not settle by gravity, even after a considerable amount of time. In fact, if the suspension is left alone for 3-5 years, a gel-like layer known as mature fine tailings (MFT) will be formed and this type of tailings is very difficult to consolidate even with current technologies.
In oil sands tailings treatment, various types of polyacrylamides (PAM) have been tested for the flocculation of tailings solids. While polyacrylamides are generally useful for fast consolidation of tailings solids, they are not selective towards fine particles and clays. As a result, the water recovered from a PAM consolidation process is rarely good enough for recycling because of high fines content in the water. Therefore, this water needs to be placed in a tailings pond where the fine particles eventually turn into MFT. Additionally, tailings treated with PAM are shear sensitive so transportation of thickened tailings to a dedicated disposal area (DDA) and general materials handling can become a challenge.
US Patent Application Publication No. 2010-0187181 (Sortwell) describes the use of zeolite to assist in the dispersion of components in aqueous mineral slurries to release and separate individual components of the slurry. Upon dispersion, Sortwell describes a process to consolidate residual mineral solids using multivalent cations and PAM.
US Patent Application Publication No. 2010-0126910 (Moffett et al.) describes the treatment of a tailings stream by contacting it with a polysilicate microgel, a polyacrylamide, a multivalent metal compound and/or a low molecular weight cationic organic polymer.
The synthesis of polysilicate microgel was described in a series of patents, including for example, U.S. Pat. No. 4,927,498 (Rushmere), U.S. Pat. No. 4,954,220 (Rushmere), U.S. Pat. No. 6,060,523 (Moffett et al.) and U.S. Pat. No. 6,274,112 (Moffett et al.).
Canadian Patent No. 2 515 581 and US Patent Application Publication No. 2006-0207946 (Scammell et al.) describe a process in which material comprising an aqueous liquid with dispersed particulate solids is transferred as a fluid to a deposition area, then allowed to stand and rigidify, in which rigidification is improved with an effective rigidifying amount of aqueous solution of a water-soluble polymer.